Solvents useful in the preparation of polymers containing hydrophilic and hydrophobic monomers

ABSTRACT

This invention relates to solvents which may be used to extract polymers that are made of hydrophilic and hydrophobic monomers

RELATED APPLICATIONS

This patent application claims priority from a provisional patentapplication, U.S. Ser. No. 60/245,518, which was filed on Nov. 3, 2000.

FIELD OF THE INVENTION

This invention relates to solvents which may be used to extract polymersthat are made of hydrophilic and hydrophobic monomers.

BACKGROUND OF THE INVENTION

Silicone hydrogels are polymers that contain both hydrophilic andhydrophobic monomers. When these polymers are used to produce contactlenses, these lenses have high oxygen permeability, good wettability,and good comfort.

Contact lenses produced from silicone hydrogels are typically made bythe following procedure. A mixture of hydrophilic and hydrophobicmonomers, as well as other components is placed in a lens mold and curedwith light. After curing, the lenses, which remain attached to eitherthe front curve or the back curve of the mold, are removed by releasingwith a suitable solvent. Typically isopropanol, water or combinationsthereof are used. After release, the lenses are extracted with alcoholsand/or other organic solvents to remove unreacted hydrophobic monomers.Typically these lenses are extracted with hexane, methylene chloride,isopropanol, or ethanol. For water immiscible solvents, those solventsare removed by evaporation/drying prior to equilibration into aqueoussolutions. For water miscible solvents, the lenses are equilibrated intoaqueous solutions. Equilibration into aqueous solution will remove anyremaining solvent, unreacted hydrophillic monomers, and hydrate thelenses. However, there are problems with this procedure.

First, when the lenses are released using alcohol or alcohol/watermixtures, the lenses swell to a level where a fragile lens, that damageseasily, is produced. Second, hydrophobic monomers have limitedsolubility in mixtures of alcohol and water, as well as some organicsolvents. Therefore to extract those monomers lenses must be extractedwith large volumes of these solvents and often the solvents must beheated. This presents problems when preparing lenses on a productionscale due to the environmental concerns of disposing of large quantitiesof used solvents. In addition, due to the low flash points of thesolvents which are currently used, heating those solvents presentsadditional hazards. Finally, the final hydration/equilibrium stepsrequire the use of 100% aqueous solvents, such as deionized water,buffer solutions, saline solutions, or other packing solutions. Whenlenses that have been extracted with alcohols and/or many organicsolvents are directly transferred to 100% aqueous solutions, there is anadditional risk of damaging the lens due to the variability of swell ofthe polymer as well as the fragility of the resulting polymer.

Therefore, there remains an unmet need for a method of processing curedpolymers that addresses one or more of the problems described above. Theinvention described herein meets that need.

DETAILED DESCRIPTION OF THE INVENTION

This invention includes a method of extracting cured polymers comprisinghydrophobic and hydrophilic monomers, where the method comprises,consists essentially of, or consists of the steps of treating the curedpolymer with an extracting solvent, wherein said extracting solvent whenmeasured at 25° C.

-   -   (a) swells the cured polymer from about 0% to about 50% and    -   (b) has Hansen Solubility Parameters within the ranges of        -   δH=about [δH_(cured polymer)+2.5] to about            [δH_(cured polymer)−8.5]        -   δP=about [δP_(cured polymer)+0.5] to about            [δP_(cured polymer)−4.0] and        -   δD=about [δD_(cured polymer)+2.5] to about            [δD_(cured polymer)−2.0].

As used herein, “cured polymers” include but are not limited to polymerscontaining hydrophobic and hydrophilic monomers, hydrogels and siliconehydrogels where silicone hydrogels are the preferred polymers, Theparticularly preferred polymers are acquafilcon A, lotrafilcon andbalafilcon A. The compositions of representative polymers are disclosedin U.S. Pat. Nos. 5,260,000; 5,998,498; 6,087,415; 5,760,100; 5,776,999;5,789,461 5,849,811; 5,965,631; U.S. patent application Ser. Nos.09/532,943; 09/652/817; and 09/957,299. These patents and patentapplications are hereby incorporated by reference for the compositionpreparation, and treatment of the polymers contained therein. Inaddition, cured polymers includes polymers that are coated withhydrophilic coating such as polyacrylic acid, HEMA and the like. Methodsof coating such polymers are disclosed in U.S. Pat. No. 6,087,415 andU.S. patent application Ser. No. 09/921,192 which is incorporated byreference in its entirety. All cured polymers of the invention may beformed into a number of useful devices which include but are not limitedto contact lenses and intraocular lenses. Methods of forming saiddevices are known and include but are not limited to molding, cutting,or lathing.

The term “monomer” refers to the building units (backbones, pendantgroups and crosslinkers) that are covalently bound to one another withinthe structure of the cured polymer. Typical hydrophobic monomers includebut are not limited to methacryloxypropyltris(trimethylsiloxy)silane(“TRIS”), monomethacryloxypropyl terminated polydimethylsiloxane(“mPDMS”), and silicone macromers as described in U.S. Pats. 5,998,498;6,087,415; U.S. patent application Ser. Nos. 09/532,943; 09/652/817; and09/957,299. Hydrophilic monomers include but are not limited ton-vinylpyrrolidone (“NVP”), N,N-dimethylacrylamide (“DMA”),2-hydroxyethyl methacrylate (“HEMA”), methacrylic and acrylic acids,vinyl lactams, acrylamides, methacrylamide, vinyl carbonate and vinylcarbamate monomers which are disclosed in U.S. Pat. No. 5,070,215, andoxazolone monomers which are disclosed in U.S. Pat. No. 4,910,277. Allaforementioned patents are hereby incorporated by reference in theirentirety. The cured polymers may contain other hydrophobic andhydrophilic components, which include but are not limited to wettingagents and the like. Although those components may be extracted by theextracting solvents of the invention, it is preferred that those agentsare not extracted by the extracting solvents of the invention.

When the cured polymers are hydrogels those polymers have the propertythat they can absorb water into the matrix of the polymer. Typicallycured polymers are treated with a solvent to remove any unreactedcomponents (ca. monomers, macromers, crosslinkers), and subsequently thepolymer is treated with an aqueous solution in order to hydrate thehydrogel. However, depending upon the solvent that was used to removethe unreacted components, the final hydration step cannot be carried outdirectly after treatment with the extracting solvent. For example, acured polymer that was extracted with hexane can not be directlyequilibrated in water without distorting the final polymer. Typicallythis problem is solved by treating the extracted polymer with a seriesof different solvents before the final aqueous equilibration step. Oneof the benefits of this invention is that when cured polymers areextracted using some of the extracting solvents of this invention, thepolymers may be directly equilibrated into aqueous media immediatelyafter extraction without using the step down procedure described above.Extracting solutions of the invention that have this advantage includebut are not limited to 85-90% DPM/DI and 85-90% TPM. This presents adistinct advantage over the known extracting solutions, because it savestime and the cost of the extra steps.

As used herein the swell of a cured polymer in a solvent is thepercentage increase in diameter of a cured polymer and may be calculatedby the either of the following formula% swell=100×[(lens diameter in extracting solvent−lens diameter inaqueous solution)/lens diameter in aqueous solution]The percentage of swell is greater than about 0 to about 50%,preferably, about 20 to about 40% and more preferably, about 25 to about35%.

In addition, the extracting solvents of the invention must have certainHansen Solubility Parameters, namely δH, δP, and δD. Those parametersare within the following rangesδH=about [δH_(cured polymer)+2.5] to about [δH_(cured polymer)−8.5]δP=about [δP_(cured polymer)+0.5] to about [δP_(cured polymer)−4.0] andδD=about [δD_(cured polymer)+2.5] to about [δD_(cured polymer)−2.0]where δH_(cured polymer), δP_(cured polymer), and δD_(cured polymer) aredetermined using the method substantially as described in CHARLES M.HANSEN, HANSEN SOLUBILITY PARAMETERS; A USERS HANDBOOK, 43-53 CRC Press2000, and CMH's SPHERE computer program for the calculations.

For example, if a cured polymer has a δH_(cured polymer) of 11.5MPa^(1/2), δP_(cured polymer) of 6.1 MPa^(1/2), and δD_(cured polymer)16.5 MPa^(1/2), the Hansen values of appropriate extraction solvents are8H about 3 to about 14, δP about 2 to about 6.6, and δD about 14.0 toabout 19.0.

The preferred extraction solvents include but are not limited tosolvents of Formula IR¹—O—[CH₂—CH(R³)—O]_(n)—R²  I

-   -   wherein    -   R¹ is hydrogen, C₁₋₆alkyl, C₁₋₆alkylcarbonyl, aminocarbonyl,        —SO₃H, phenyl, or substituted phenyl where the phenyl        substituents are C₁₋₆alkyl, C₁₋₆alkoxy, amino, nitro, or        halogen;    -   R² is hydrogen, C₁₋₆alkyl, C₁₋₆alkylcarbonyl, aminocarbonyl,        —SO₃H phenyl, or substituted phenyl where the phenyl        substituents are C₁₋₆alkyl, C₁₋₆alkoxy, amino, nitro, or        halogen;    -   R³ is hydrogen, C₁₋₆alkyl phenyl, C₁₋₆alkylcarbonyl,        aminocarbonyl, —SO₃H, phenyl, or substituted phenyl where the        phenyl substituents are C₁₋₆alkyl, C₁₋₆alkoxy, amino, nitro, or        halogen; and    -   n is 1-10.

The preferred R¹ is selected from the group consisting of C₁₋₆alkyl andC₁₋₆alkylcarbonyl, where the more preferred R¹ is selected from thegroup consisting of C₁₋₆alkyl, and the particularly preferred R¹ ismethyl. The preferred R² is selected from the group consisting ofC₁₋₆alkyl and C₁₋₆alkylcarbonyl, where the more preferred R² is selectedfrom the group consisting of C₁₋₅alkylcarbonyl, and the particularlypreferred R is acetyl or hydrogen. The preferred R³ is selected from thegroup consisting of C₁₋₅alkyl and C₁₋₆alkylcarbonyl where the morepreferred R³ is C₁₋₆alkyl, and the particularly preferred R³ ishydrogen. The preferred n is 1-5.

Examples of extracting solvents include but are not limited to ethyleneglycol-n-butyl ether, diethylene glycol-n-butyl ether, diethylene glycolmethyl ether, ethylene glycol phenyl ether, propylene glycol methylether, dipropylene glycol methyl ether, tripropylene glycol methylether, propylene glycol methyl ether acetate, dipropylene glycol methylether acetate, propylene glycol-n-propyl ether, dipropyleneglycol-n-propyl ether, tripropylene glycol-n-butyl ether, propyleneglycol-n-butyl ether, dipropylene glycol-n-butyl ether, tripropyleneglycol-n-butyl ether, tripropylene glycol-n-propyl ether, proplyeneglycol phenyl ether, dipropylene glycol dimethyl ether, propyl acetate,and methyl isobutyl ketone. The particularly preferred extractingsolvents are butyl acetate, dipropylene glycol methyl ether acetate(DPMA), diproplyeneglycol methyl ether (DPM), dipropyleneglycol dimethylether (DMM), tripropylene glycol methyl ether (TPM), and mixturesthereof. In addition the particularly preferred solvents mixtures ofDPMA, DMM, DPM, or TPM with water or propylene glycol. The mostpreferred solvent for a cured polymer having δH_(cured polymer) of 11.5MPa^(1/2), P_(cured polymer) of 6.1 MPa, and δD_(cured polymer) 16.5MPa^(1/2) is dipropylene glycol methyl ether acetate.

As stated above, the choice of extracting solvent is driven by thephysical properties of the cured polymer. More than one component canused in the extracting solvent, where, depending upon the physicalproperties of the cured polymer, it is preferable that the extractingsolvent contain two or more components. For example if the cured polymeris a silicone hydrogel where the majority of its surface is hydrophobic,it would be preferred to use a combination of a hydrophobic solventhaving relatively low hydrogen bonding affinity with a hydrophilicsolvent having low molecular weight and high hydrogen bonding affinity.The majority of said extracting solvent contains the hydrophobic solventwhere the percentage of hydrophobic solvent is about 20 to about 98%(percent by weight), more preferably about 70 to about 98%, mostpreferably about 80 to about 90%. The molecular weight of thehydrophilic solvent of this extracting solvent is about 15 to about 200Daltons, more preferably about 15 to about 100 Daltons. Examples of suchsolvents include 90:10 (parts by weight), DPMA:DI, 90:10 DMM:DI, 90:10DPMA:propylene glycol, 90:10 DMM:propylene glycol. In these examplesDPMA and DMM are the hydrophobic solvents having low hydrogen bondingaffinity, while propylene glycol and Dl are the hydrophilic solventshaving high hydrogen bonding affinity and low molecular weights.

If the cured polymer is a silicone hydrogel where its hydrophobicsurface is coated with a hydrophilic polymer such as polyacrylic acid orpoly HEMA, it would be preferred to use solvent mixtures that containhydrophobic solvents that have moderately high hydrogen bonding affinityand hydrophilic solvents having low molecular weight and relatively highhydrogen bonding affinity. The majority of said extracting solventcontains the hydrophobic solvent where the percentage of hydrophobicsolvent is about 20 to about 98% (percent by weight), more preferablyabout 70 to about 98%, most preferably about 80 to about 90%70 to about98% (percent by weight), more preferably about 80 to about 90%. Themolecular weight of the hydrophilic solvent of this extracting solventis about 15 to about 200 Daltons, more preferably about 15 to about 100Daltons. Examples of such solvents include 90:10, TPM:DI, 90:10 DPM:DI,90:10 TPM:propylene glycol, 90:10 DPM:propylene glycol. In theseexamples TPM and DPM are hydrophobic solvents and propylene glycol andDI are the low molecular weight solvents having relatively high hydrogenbonding affinity.

Although the choice of extracting solvent is critical to this invention,the method may be improved by adjusting certain physical parameters. Forexample, a greater percentage of unreacted hydrophobic monomers can beremoved by raising the temperature of the solvent, agitating saidsolvent, increasing the time of the extraction procedure and anycombination thereof.

Further the invention includes a method of releasing and extractingcured polymers comprising hydrophobic and hydrophilic monomers, wherethe method comprises, consists essentially of, or consists of the stepsof treating the cured polymer with an extracting solvent, wherein saidextracting solvent when measured at 25° C.

(a) swells the cured polymer to at least 15%, and

-   -   (b) has Hansen Solubility Parameters within the ranges of    -   δH=about [δH_(cured polymer)+2.5] to about        [δH_(cured polymer)−8.5]    -   δP=about [δP_(cured polymer)+0.5] to about [δP_(cured polymer)        −4.0] and    -   δD=about [δD_(cured polymer)+2.5] to about        [δD_(cured polymer)−2.0].        The terms hydrophobic and hydrophilic monomer and extracting        solvent have their aforementioned definitions and preferred        ranges. The preferred polymers are contact lenses and        intraocular lenses.

Still further the invention includes a polymer that is made by a methodof extracting cured polymers comprising hydrophobic and hydrophilicmonomers, where the method comprises, consists essentially of, orconsists of the steps of treating the cured polymer with an extractingsolvent, wherein said extracting solvent when measured at 25° C.

-   -   (a) swells the cured polymer from about 0% to about 50%, and    -   (b) has Hansen Solubility Parameters within the ranges of    -   δH=about [δH_(cured polymer)+2.5] to about        [δH_(cured polymer)−8.5]    -   δP=about [δP_(cured polymer)+0.5] to about        [δP_(cured polymer)−4.0] and    -   δD=about [δD_(cured polymer)+2.5] to about        [δD_(cured polymer)−2.0]

In order to illustrate the invention the following examples areincluded. These examples do not limit the invention. They are meant onlyto suggest a method of practicing the invention. Those knowledgeable inpolymers as well as other specialties may find other methods ofpracticing the invention. However, those methods are deemed to be withinthe scope of this invention. All of the references cited in thisapplication are hereby incorporated by reference.

EXAMPLES

The following abbreviations were used in the examples

-   IPA=isopropanol-   DI=deionized water-   DMM=dipropylene glycol dimethyl ether-   DPMA=dipropylene glycol methyl ether acetate-   DPM=dipropylene glycol methyl ether-   TPM=tripropylene glycol methyl ether-   Macromer A=the macromer substantially prepared as described in    Example-   25 of U.S. patent application Ser. No. 09/957,299-   mPDMS=monomethacryloxypropylterminated polydimethylsiloxane (MW    800-1000)

Example 1 Evaluation of DPMA and IPA as Extracting Solvents

The ability of DPMA to serve as an effective extracting solvent wasevaluated by examining levels of unreacted hydrophobic monomers fromcured lenses. A residual level is defined as the amount of monomer(s)that remain unreacted or unpolymerized after a lens is adequately cured.The monomer mixture that comprises acquafilcon A was loaded to 7 frames(56 lenses) and cured for 8 minutes to 60 minutes, at 55-70° C., usingdimethyl-3-octanol as a diluent and visible light (visible lightwavelength: 380-460 nm with a peak maximum at 425 nm, dose: approx. 2.5J/cm²). The resulting lenses were de-molded (lenses on front curve), andremoved from the frames using tweezers.

Five lenses were accurately weighed into five individual glassscintillation vials and 5 mL of DPMA (DOWANOL®) was pipetted into eachvial. Vials 1 though 5 were sonicated for 1 hr at 25, 35, 50, 60, and70° C., respectively. Concurrent experiments were set up using iPA asthe extracting solvent. The resulting extracts were analyzed formacromer and mPDMS and the levels (weight percent) obtained aretabulated in Tables 1 and 2. The samples were analyzed for thesemonomers because they are the most hydrophobic components in the finalpolymer. These figures show that DPMA extracts these hydrophobicmonomers at a level which is comparable to IPA over a range oftemperatures, where the levels are most comparable at 60° C. and 70° C.TABLE 1 Temperature and Solvent Effects on Residual Macromer Extractionfrom Lenses DPMA IPA Temp: ° C. % [by lens weight] % [by lens weight] 250.355 0.486 35 0.460 0.549 50 0.480 0.566 60 0.524 0.586 70 0.519 0.565

TABLE 2 Temperature and Solvent Effects on Residual mPDMS Extractionfrom Lenses DPMA IPA Temp. ° C. % [by lens weight] % [by lens weight] 250.477 0.490 35 0.472 0.491 50 0.475 0.484 60 0.486 0.503 70 0.490 0.486

Example 2 Temperature on Leachable Levels of Hydrophobic Monomers fromCured Polymers with DPMA

This experiment determines the level of leachable hydrophobic monomerswhich can be obtained from cured polymers that were extracted with DPMA.A leachable level is defined as the amount of a monomer (or monomers)obtained after a polymer has been cured, extracted and hydrated andthen, subsequently extracted with another solvent. Typically thesubsequent extraction solvent is iPA. The monomer mixture that comprisesacquafilcon A was loaded to frames and cured for 8 minutes to 60minutes, at 55-70° C., using dimethyl-3-octanol, as a diluent andvisible light (visible light (wavelength: 380-460 nm with a peak maximumat 425 nm, dose: approx. 2.5 J/cm²). The resulting lenses, 3 frames (24lenses) were de-molded (lenses on front curve), strapped to cyclicolefin copolymer (TOPAS®) leaching/hydration vehicles and placed in ajacketed 1 L beaker, controlled by a circulating water heater/cooler.The extracting solvent, DPMA (850 mL) was added (˜35 mL/lens) andagitated by a magnetic stirrer for 90 min at 25° C. At the end of theextraction, the vehicles (with frames and lenses) were placed inde-ionized water at 15° C., controlled by a circulating waterheater/cooler. The water was agitated by circulation at high speed usingan immersion water circulator. After 1 hr, 10 lenses were withdrawn,blotted dry and accurately weighed into a scintillation vial. Five mL ofiPA was added to the vial and the vial was sonicated for 1 hr. Sampleswere prepared in duplicate and analyzed for leachable mPDMS 1000 andmacromer. Concurrent experiments were run using DPMA as the extractingsolvent at temperature of 35, 50, 60, and 70° C., respectively. Theresults of these experiments are tabulated in Table 3. The results showthat at all temperatures, the leachable level for mPDMS is less than 175ppm (mg/Kg on a lens wt. basis). Typically levels of 600-1000 ppm areobtained when iPA is used as the initial extracting solvent. The levelof leachable macromer decreases with increasing extraction temperatureand leachable levels at 60° C. and 70° C. are comparable with levelsobserved for IPA (600-1000 ppm). This finding demonstrates that there isa significant advantage in using DPMA as an extraction solvent ratherthan IPA. In a production environment, due to IPA's low flash point (12°C.) and high vapor pressure (45.8 mmHg @ 25° C.). However, due to DPMA'shigh flash point (187° C.) and low vapor pressure (0.08 mmHg @ 20° C.)this solvent may be used at elevated temperatures without theaccompanying safety hazards. TABLE 3 Temperature Effect on LeachablemPDMS and Macromer Extraction with DPMA Temp. ° C. mPDMS (mg/Kg)Macromer (mg/Kg) 25 <175 2732 35 <175 1250 50 <175 862 60 <175 656 70<175 581

Example 3 Analysis of Leachable Levels of Hydrophobic Monomers fromCured Polymers with DMM

This experiment determines the level of leachable hydrophobic monomerswhich can be obtained from cured polymers, initially processed orextracted with DMM. In example 2, extraction was accomplished in acyclic olefin copolymer (TOPAS®) leaching/hydration vehicles, whereas inthis example extraction was done in scintillation vials. The monomermixture that comprises acquafilcon A was loaded to the frames and curedfor 8 minutes to 60 minutes, at 55-70° C., using dimethyl-3-octanol, asa diluent and visible light (visible light (wavelength: 380-460 nm witha peak maximum at 425 nm, dose: approx. 2.5 J/cm²).

Ten lenses were removed from frames and placed into each of 6scintillation vials. 10 mL DMM (1 mL per lens, PROGLYDE®) was added toeach vial and shaken for 30 minutes at 175 rpm on a Thermolyne Type50000 Maxi-mix III. At the end of this period, lenses from vial 1 wereequilibrated in 250 mL DI water, by shaking for 1 hr at 175 rpm. Afterequilibration, the 10 lenses were harvested, blotted dry and accuratelyweighed into a scintillation vial. Five mL of isopropanol was added tothe vial and the vial was sonicated for 1 hr. The iPA extract wasanalyzed for leachable mPDMS and macromer. The DMM from the remainingvials were decanted, and 10 mL aliquot of fresh DMM was added to eachvial. The vials were shaken for 10 minutes, which constituted “1 cycle”.The procedure was repeated to generate samples after 5 cycles, withfresh DMM replacing the extract at the start of each cycle. Followingeach cycle, lenses were equilibrated in Dl water and subsequentlyextracted with iPA as described above. The iPA extracts were analyzedfor leachable mPDMS and macromer. The data is tabulated in Table 4.TABLE 4 mPDMS and Macromer Extraction using DMM (Residual levels -mPDMS: 6706 mg/Kg, macromer: 7184 mg/Kg) Time (min)/Cycle mPDMS (mg/Kg)Macromer (mg/Kg) 30 1031 2678 40/Cycle 1 <225 1879 50/Cycle 2 <225 180760/Cycle 3 <225 1595 70/Cycle 4 <225 1513 80/Cycle 5 <225 1531

Example 4 Comparison of % Swell of Cured Polymer in a Variety ofSolvents

The procedure for testing the swell of a polymer in a number of testingsolvents is described in this example. The monomer mixture ofacquafilcon A was dosed into molds and cured for 8 minutes to 60minutes, at 55-70° C., using dimethyl-3-octanol, as a diluent andvisible light (visible light (wavelength: 380-460 nm with a peak maximumat 425 nm, dose: approx. 2.5 J/cm²). The resulting discs, (thicknessrange of 70-110 μm) were fully hydrated by releasing from the molds in60:40 isopropanol (IPA)/deionized (DI) water, extracting additionalresidual monomers using five aliquots of 100% IPA over a period of tenhours (two hours/aliquot) and then equilibrated in deionized water.These lenses were then equilibrated in the various testing solvents aswell as physiological saline. Measurements of lens' diameters were madeand a comparison of % swell made. The % swell was calculated using thefollowing equation:% swell=100×[(lens diameter in extracting solvent−lens diameter inphysiological saline)/lens diameter in physiological saline]

The data for % swell at 25° C. is tabulated in Table 5. In addition,since the volatility and flammability for DPMA is relatively low, thisparticular solvent could be utilized at higher processing temperatures.The matrix swell of the polymer in DPMA, over the temperature rangeinvestigated (25-70° C.), was determined and found to be linear. TABLE 5% Swell in Various Test Solvents Test Solvent % Swell PhysiologicalSaline 0 DI Water 0.56 IPA 52.36 n-Butyl Acetate 31.12 Proglyde DMM*29.83 Dowanol DPMA* 24.24 Dowanol DPMA @ 35° C. 26.84 Dowanol DPMA @ 50°C. 30.74 Dowanol DPMA @ 60° C. 31.91 Dowanol DPMA @ 70° C. 34.91

Example 5 Comparison of % Swell of Coated Cured Polymer in a Variety ofSolvents

Contact lenses coated with poly HEMA were prepared as described inExample 14 of U.S. patent application Ser. No. 09/921,192. Using themethod of Example 4, the lenses were released and equilibrated in threedifferent solvent mixtures. For this example only, the swell wascalculated using the following formula, where the diameter of the lensmold is the diameter of the mold that forms the cured article% swell_(lens mold method)=100×[(lens diameter in extractingsolvent−diameter lens mold)/diameter lens mold]

Calculating the swell by this method results in a percentageswell_(lens mold method) that is from about 1 to about 5%, preferablyabout 1 to about 2% greater than calculating the percent swell using thediameter of the polymer in an aqueous solution. 100% DPM, 100% TPM,90:10 DPM:DI, 90:10 TPM:DI, and 90:10 IPA:DI were tested at 60° C. andthe percentage swellens mold method was 49.3%, 46.5%, 26.5%, 17.3%, and51% respectively. A summary of the data collected for the percentage ofswell in different solvent systems is presented in Tables 6, 7, and 8below. This data shows that aqueous mixtures of TPM and DPM are thepreferred solvents for extracting a poly HEMA coated lens. TABLE 6 DPMSolvent System @ 60° C. (remainder H₂O) Solvent CompositionSwell_(lens mold method) (%) 100 49.3 95 35.7 90 26.5 85 19.9

TABLE 7 TPM Solvent System @ 60° C. (remainder H₂O) Solvent CompositionSwell_(lens mold method) (%) 100 46.5 95 28.8 90 17.3 85 12.6

TABLE 8 TPM Solvent System @ 80° C. (remainder H₂O) Solvent CompositionSwell_(lens mold method) (%) 100 42.3 95 36.1 90 22.3 85 15.6

Example 6 Hydration of Lenses

This procedure demonstrates that lenses extracted using a solvent withlimited solubility in aqueous solutions, such as DPMA may beequilibrated directly to aqueous solution without inducing internalstresses. Use of IPA as an extraction solvent yielded lenses with alarge variation in final lens' diameter uniformity even with a step-downgradient. A longer, slower step-down gradient from IPA to aqueoussolution was examined and the lenses found to have a tighter statisticaldistribution for lens' diameter. Lenses extracted in DPMA andequilibrated directly to aqueous solution also demonstrated a tighterdistribution, removing the necessity of the additional processing step.

The monomer mixture of acquafilcon A was dosed into molds and cured for8 minutes to 60 minutes, at 55-70° C., using dimethyl-3-octanol, as adiluent and visible light (visible light (wavelength: 380-460 nm with apeak maximum at 425 nm, dose: approx. 2.5 J/cm²):

-   -   60:40, IPA/DI water release from molds, extraction in 100% IPA        and a step-down gradient to aqueous solution equilibration in        increments of 30, 60, 100%.    -   60:40, IPA/DI water release from molds, extraction in 100% IPA        and a step-down gradient to aqueous solution equilibration in        increments of 10, 20, 30, 40, 50, 75, 100%.    -   100% DPMA release and extraction and direct aqueous        equilibration.

Measurement of lens' diameters on 10 lenses were made in both x and ydirection (to pick up any lenses that might be out-of-round) for eachcondition. The diameter data is presented in Table 9. TABLE 9 Comparisonof Extraction/Equilibration Condition Hydration Dia. x Dia. Avg.Conditions Lens # (mm) Dia. y (mm) (mm) 60:40 DI/IPA 1 14.177 14.31414.246 Release 2 14.150 14.152 14.151 IPA Extraction 3 14.171 14.16514.168 Abbreviated Step- 4 14.179 14.208 14.194 Down 5 14.152 14.22214.187 6 14.170 14.154 14.162 7 14.227 14.177 14.202 8 14.144 14.18814.166 9 14.179 14.194 14.187 10  14.345 14.183 14.264 Avg 14.189 14.19614.193 Std 0.059 0.047 0.052 Max 14.345 14.314 14.345 Min 14.144 14.15214.144 Range 0.201 0.162 0.201 60:40 IPA/DI 1 14.111 14.163 14.137Release 2 14.112 14.148 14.130 IPA Extraction 3 14.108 14.159 14.134Gradual Step-Down 4 14.128 14.125 14.127 5 14.149 14.119 14.134 6 14.13514.170 14.153 7 14.186 14.136 14.161 8 14.129 14.138 14.134 9 14.14414.126 14.135 10  14.128 14.081 14.105 Avg 14.133 14.137 14.135 Std0.023 0.026 0.024 Max 14.186 14.170 14.186 Min 14.108 14.081 14.081Range 0.078 0.089 0.105 DPMA Release 1 14.597 14.606 14.602 DPMAExtraction 2 14.615 14.610 14.613 Direct Equilibration 3 14.591 14.58814.590 4 14.614 14.616 14.615 5 14.614 14.613 14.614 6 14.602 14.58614.594 7 14.612 14.610 14.611 8 14.599 14.604 14.602 9 14.591 14.58914.590 10  14.588 14.593 14.591 Avg 14.602 14.602 14.602 Std 0.011 0.0110.011 Max 14.615 14.616 14.616 Min 14.588 14.586 14.586 Range 0.0270.030 0.030

Example 7 Release of Lenses Using a Variety of Extraction Solvents

The monomer mixture of acquafilcon A was dosed into molds and cured for8 minutes to 60 minutes, at 55-70° C., using dimethyl-3-octanol, as adiluent and visible light (visible light wavelength: 380-460 nm with apeak maximum at 425 nm, dose: approx. 2.5 J/cm²). Subsequently, thelenses were subjected to a variety of solvents to release the lensesfrom the molds. The four groups of solvents utilized were IPA, 60:40IPA/DI, DMM and DPMA and the release was conducted at ambienttemperature. The time necessary for the lenses to release from the moldsand the physical characteristics during release were observed andrecorded. The data presented in Table 10, shows that both DMM and DPMAhave distinct advantages over IPA or IPA in combination with DI (whichhas an equivalent % swell to DPMA) due to the time of release and/or thephysical manner of release of the lenses. TABLE 10 Comparison of LensRelease Release Time Solvent (min) % Swell Physical Appearance IPA <1052 Lenses swell rapidly forming wrinkles and folds and often creatingstress at the interface with the mold, resulting in fractures in thelenses. 60:40 60-90 25 Lenses swell first in IPA/DI the center (thethinner portion of the lens), form wrinkles & folds and then pull freefrom the edges. DMM 20-30 30 Lenses swell relatively slowly anduniformly throughout the bulk of the lens, resulting in a uniformrelease from the mold. DPMA 20-30 24 Lenses swell relatively slowly anduniformly throughout the bulk of the lens, resulting in a uniformrelease from the mold.

Example 8 Release of Coated Lenses Using a Variety of ExtractionSolvents

Contact lenses coated with poly HEMA were prepared as described inExample 14 of U.S. patent application Ser. No. 09/921,192. Using themethod of Example 7, the lenses were released from the molds andequilibrated in the solution for about 2 hours. The temperature, releasetime swell and amount of extracted residuals were recorded in Table 11.Immediately after release from the mold materials the lenses exhibitedsome physical distortion (wrinkled edges). However lenses in all testedsolutions equilibrated within 15-20 minutes after release to give smoothrounded lenses. This example proves that lenses released and extractedwith the tested solvents swell far less than lenses released andextracted with IPA. In addition, this demonstrates that lenses extractedwith these extracting solvents may be equilibrated directly into waterwithout using a step down procedure. TABLE 11 Solvent System ReleaseSwell (%) (remainder Temperature Time (lens target Leachables H₂O) (°C.) (min) dia. 14.2 mm) (mg/Kg) 85% DPM 60 22 19.9 mPDMS <285 Macromer4603 Tris 0.77 HCPK 2.47 Norblock <3 90% DPM 60 18 26.5 mPDMS <286Macromer 4087 Tris 1.61 HCPK 2.13 Norblock <3 85% TPM 60 53 12.6 mPDMS568 Macromer 4961 Tris 1.98 HCPK 1.00 Norblock <3 85% TPM 80 18 15.6mPDMS <289 Macromer 5046 Tris 1.78 HCPK 1.99 Norblock <3 90% TPM 80 2622.3 mPDMS 860 Macromer 4964 Tris 2.28 HCPK 1.13 Norblock <3 90% TPM 6030 17.3 mPDMS 335 Macromer 4428 Tris 1.55 HCPK 0.9 Norblock <3

1-11. (Cancelled)
 12. A method of releasing and extracting curedpolymers comprising hydrophobic and hydrophilic monomers, where themethod comprises the steps of treating the cured polymer with an aliquid extracting solvent, wherein said extracting solvent when measuredat 25° C. (a) swells the cured polymer to at least about 15%, and (b)has Hansen Solubility Parameters within the ranges of δH=about[δH_(cured polymer)+2.5] to about [δH_(cured polymer)−8.5] δP=about[δP_(cured polymer)+0.5] to about [δP_(cured polymer)−4.0] and δD=about[δD_(cured polymer)+2.5] to about [δD_(cured polymer)−2.0]. 13-14.(Cancelled)
 15. The method of claim 12 wherein δH is about 3.0 to about14, δP is about 2 to about 6.6 and δD is about 14.0 to about
 19. 16-20.(Cancelled)
 21. The method of claim 12 wherein said cured polymer is acontact lens.
 22. The method of claim 12 wherein the swell of the curedpolymer is about 15% to about 40%.
 23. A polymer that is prepared by amethod of extracting cured polymers comprising hydrophobic andhydrophilic monomers, where the method comprises the steps of treatingthe cured polymer with a liquid extracting solvent, wherein saidextracting solvent when measured at 25° C. (a) swells the cured polymerfrom about 0% to about 50% and (b) has Hansen Solubility Parameterswithin the ranges of δH=about [δH_(cured polymer)+2.5] to about[δH_(cured polymer)−8.5] δP=about [δP_(cured polymer)+0.5] to about[δP_(cured polymer)−4.0] and δD=about [δD_(cured polymer)+2.5] to about[δD_(cured polymer)−2.0]. 24-25. (Cancelled)
 26. The method of claim 12wherein δH is about 3.0 to about 14, δP is about 2 to about 6.6 and δDis about 14.0 to about
 19. 27-31. (Cancelled)